The present invention relates to medical monitoring devices and, in particular, it relates to a monitor for the detection of sleep apnea.
It is known that sleep related breathing disorders are a common medical problem. Two common sleep pathology syndromes are Obstructive Sleep Apnea (OSA) and Central Sleep Apnea (CSA).
Obstructive Sleep Apnea (OSA) occurs when the upper airway (the nose, mouth or throat) become obstructed in some way during sleep, and is usually accompanied by a decrease in the oxygen saturation of the blood (SpO2). Snoring indicates an intermittent obstruction, which at times may become complete, stopping air flow. Apnea (the cessation of breathing) may occur hundreds of times during one night of sleep, leading to severe sleep disruption and excessive daytime somnolence. As such, the patient may easily fall asleep during working hours, such as when the patient is driving a car or a truck. Many commercial trucking firms thus require that their drivers undergo sleep studies to determine if they suffer from OSA. Furthermore, OSA may cause heart problems such as cardiac arrhythmias and Cor Pulmonale.
Central Sleep Apnea Syndrome (CSA), in contrast, occurs due to a defect in central nervous system control of the respiratory drive, and is most commonly seen in patients with neurological disorders affecting respiratory control and in the elderly. CSA may also result in frequent awakenings and their associated impact on daytime performance.
Definitive diagnosis of these respiratory-sleep pathologies is currently achieved by means of an in-lab, full night, formal sleep study. In such a study, the patient is required to sleep for a whole night in a controlled environment (a xe2x80x9csleep laboratoryxe2x80x9d) while connected to multiple monitoring devices, which continuously measure such physiological parameters as respiratory effort, nasal and oral airflow, brain electrical activity (EEG), muscle electrical activity (EMG), heart rate and rhythm (ECG), and blood oxygen saturation. These parameters are recorded on paper or stored in a memory bank for later analysis. A trained sleep technician is required to oversee the study so as to ensure that all parameters are recorded properly. The data is then analyzed, either manually or by specialized software, to produces a xe2x80x9chypnogramxe2x80x9d which describes the nature of the patients sleep. Indices in the hypnogram, such as an xe2x80x9capnea indexxe2x80x9d and a xe2x80x9cleg movement indexxe2x80x9d, are then used, by a sleep specialist, to diagnose the patients pathology.
The formal sleep study as a means of diagnosing and following-up patients with respiratory related sleep problems, however, suffers from several deficiencies and limitations:
1. The study requires the use of multiple medical monitoring devices and the continuous presence of a trained technician. It is thus labor intensive to perform, and requires the use of multiple, expensive, resources.
2. The patient is asked to sleep in a non natural sleep environment, which may itself affect his sleep patterns.
3. The patient is inconvenienced by having to be in a hospital setting for a night.
4. There is no patient privacy.
As such, sleep laboratories are a limited resource, each containing only a limited number of beds. This is particularly problematic as studies are often conducted on xe2x80x9csuspiciousxe2x80x9d patients in whom the outcome is frequently negative. In such patients, for whom there was no need for the study at all, a limited screening study may have been sufficient to exclude sleep pathology. The study price often prohibits repeating studies on a regular basis for purposes of patient follow-up.
In order to overcome some of these drawbacks, the performance of home studies by means of ambulatory systems has become popular. These studies utilize miniature ambulatory recorders, and are limited to a relatively small number of information recording channels. The patient is prepared for the study at the sleep lab, and returns home with all sensors appropriately attached. Alternatively, a technician may come to the patients home, or the patient may attach the sensors by himself after receiving appropriate instruction from a technician. The study is then conducted in the patient""s home, as he sleeps in his own bed, and the recorded data stored in a memory device. In the morning the recorder and memory device are returned to the sleep lab for data downloading to an analysis station. Some of these ambulatory systems can correct for some data recording problems, by adjusting the gain or filtering during data recording or when post-processing the data. Alternatively, the study can be monitored from the sleep lab via a modem.
Although ambulatory sleep-apnea monitoring systems are much more convenient to the patient, and considerably less expensive than formal, in-lab, sleep studies, all current ambulatory sleep monitoring systems suffer from several deficiencies:
1. Performance of the study still requires the participation of a trained technician (for the purposes of either attaching the monitoring device or instructing the patient how to do so) and the participation of a formal sleep laboratory (for the purposes of downloading and analyzing the test results, and maintaining the equipment necessary for the performance of the test). Such tests are thus still labor and resource intensive.
2. As analysis of the recorded data is performed off-line in the sleep laboratory, the ambulatory monitoring device must be able to store all registered data in a suitable memory storage device, until such data can be downloaded. Alternatively, if the data is relayed to the sleep laboratory in real time, a modem and telephone line are necessary. Current ambulatory devices are therefore relatively complex and expensive to manufacture. As such, ambulatory studies are still too expensive to perform on a regular basis (currently approximately $500 per study), thus precluding their widespread use as a screening tool or for purposes of frequent patient follow-up. In addition, the cost of such studies does not justify their use on xe2x80x9cdifficultxe2x80x9d patients, such as mental health patients or small children, in whom the likelihood of technical failure of the study is high.
There is therefore a need for a sleep-apnea screening system which is suitable for widespread use for patient screening and follow-up. Such a system should be sufficiently simple to implement as to allow patients to perform the study at home, without the need for assistance from a trained technician. In addition, such a system should provide the patient with an easily understandable result at the end of the study, without the need for data processing at a sleep laboratory, and without the need for interpretation of the result by a physician or technician. Finally, such a system should be sufficiently inexpensive as to make multiple and frequent studies practical to finance.
The present invention is an ambulatory sleep-apnea screening system. The invention integrates a minimal data collection and analysis system into a disposable, single use device that achieves data collection and analysis in real time, and outputs the study result in an easily understood format immediately following the study. The entire system is incorporated into a single small, flexible, plastic unit which can be easily positioned, or placed, under the patients nose, that is, upon the patients philtrum. The system is powered by a lithium battery, which is irreversibly activated by means of the patient pulling on a tab. Once activated, a respiration detector (such as that which measures temperature differences in an airflow, by which is meant a flow of inhaled and exhaled nasal or oral air) inputs data describing the pattern of respiration into a micro-processor, via an analog to digital converter. A flashing LED display indicates to the user that the device is correctly positioned. A software module detects the absence of hot airflow for a predetermined periodxe2x80x94indicating apnea. Apnea duration is measured, normal breaths between apneas are counted, and, together with real-time clock information, the presence, and severity of, episodes of apnea is documented. Data can be sampled continuously, or in segments each a few minutes long, so as to conserve battery power. After a predefined period of time, non volatile output flags (in the form of heat sensitive colored dots) are set by the software. Once activated, the output flags undergo a permanent color change. As such, they produce an easily read hard copy of the study results, informing the user whether significant apnea was detected and whether a physician need be consulted. Hereinafter, output flags which undergo a permanent change in color when activated by heat are referred to as xe2x80x9cheat sensitive permanent color display elementsxe2x80x9d.
The integration, onto a respiratory sensor, of a sleep apnea screening system which is capable of analyzing respiratory data in real time and generating an immediate report thereof, is unique to the current invention. By xe2x80x9creal timexe2x80x9d is meant that the processing of the respiratory data and the sensing of the respiratory pattern occur during the same time interval, rather than the processing occurring after all respiratory sensing has been completed.
As data is analyzed in real time, the need for a large memory storage unit to store data for later analysis, and the need for complex downloading hardware, are obviated. This feature allows the entire system to be manufactured in a small and inexpensive format, and provides the user with the result of the study immediately upon conclusion of the study, without the need for data processing and analysis by medical professionals at a sleep laboratory. Furthermore, as the power source, processor, and display mechanism of the device are all integrated with the respiratory sensor into a small, single, unit, without the need for cables or wires connecting these components to each other, and as an easily seen flashing light confirms to the user that placement and operation of the device are correct, the device is simple and straightforward to use. The device can thus be operated without supervision by trained medical professionals. Accordingly, the cost per study is sufficiently low as to justify performing studies frequently for screening purposes (whenever there is even a slight chance of true pathology being present) or for regular patient follow-up. As their are no cables or wires connecting the respiratory sensor with the rest of the device, the possibility that the sensor might be pulled of off the users face, due to the cable becoming entangled while the user is asleep, is obviated.
It is an object of the current invention to provide a sleep apnea screening system which can be easily and reliably used by a patient without the need for professional supervision.
It is a further object of the current invention to provide a sleep apnea screening system which does not require the use of complex data storage and analysis hardware.
It is an additional object of the current invention to provide a sleep apnea screening system which is sufficiently simple and inexpensive as to facilitate performance of multiple sleep apnea screening studies on the same patient, on unreliable patents, or on patients with a low likelihood of having real pathology.
It is a vet further object of the current invention to provide a sleep apnea screening system which allows the study to be performed in the patients natural sleep environment.
It is a yet further object of the current invention to provide a sleep apnea screening system which does not infringe patient privacy.
According to the teachings of the present invention there is provided a sleep apnea screening system, including a respiration sensor, for sensing a respiratory pattern, at a location on a respiratory tract: a processor, for analyzing the respiratory pattern to determine the presence of a pattern of apnea, and for correlating the pattern of apnea with a diagnosis; a display, for displaying the diagnosis; a power source, for powering the respiration sensor, the processor, and the display; and a housing, for housing the processor, the display, and the power source, on the respiration sensor, the housing being placeable at the location on the respiratory tract. There is also provided a sleep apnea screening method, including the steps of placing a housing at a location on a respiratory tract; sensing a respiratory pattern at the housing during a time interval; processing the sensed respiratory pattern to detect the presence of a pattern of apnea, the processing occurring during the time interval; correlating the pattern of apnea with a diagnosis, the correlating occurring during the time interval; and displaying the diagnosis on the housing.